1. Field of the Invention
This invention relates to a shrink packaging apparatus for use in packaging dry cells and other articles with a film held in contact with their outer surface.
2. Description of the Prior Art
Shrink packaging techniques have been known including, as a typical example, the one described in Japanese Patent Publication No. 56-12533 (Published: Mar. 23, 1981; Application No. 51-126979; Filed: Aug. 21, 1976; Applicant: Tokiwa Kogyo, Ltd.; Inventor: Chuji Noh).
This prior-art technique is such that, as FIG. 11 illustrates, a beltlike heat-shrinkable film 4 having spaced lines of perforations 7 is formed into a tubular shape in a former 5 and articles 9 are then fed into the tubulated film 4 which, in turn, is transported into a tunnel-shaped heating unit 26e while containing the articles 9 therein for being heated in the tunnel.
According to this technique, the film 4 is shrunk by heating so that it can be autocut along each line of perforations 7 under tension due to shrinkage. Cut film ends can be set in intimate contact with the front and rear sides 9a, 9b of each article 9 by subsequent heating.
Therefore, according to such technique, in which the film 4 is subject to no mechanical cutting, impact due to film cutting is insignificant and there falling of articles 9 is prevented. Additionally, since the film 4 is cut while being shrunk, cut film ends have greater tension to provide substantially great strength for enabling the film to cover and hold sides of the article 9. Therefore, the technique permits assembly packaging of a plurality of articles 9 . . . as illustrated in FIG. 12.
However, from the standpoint of practical application, the prior art technique involves a number of problems as pointed out below.
In order to carry out heat shrinking and cutting of the film 4 properly in shrink packaging, it is necessary that the entire surface of the film 4 surrounding the article 9 must be thoroughly and uniformly heated by the heating unit 26e.
However, with the prior-art technique, in which each article 9 is fed into the tunnel-like heating unit 26e as it is placed on a conveyor 40, the botton portion of the article 9 in contact with the conveyor belt cannot be as effectively heated as the other sides of the article 9. Moreover, the film portion at the bottom of the article 9 which is in direct contact with the conveyor belt is prevented from proper shrinking because of possible friction due to its contact with the conveyor belt. Therefore, film shrinkage at the bottom of the article 9 is lower than that at the top and other sides of the article 9, which fact has made it difficult to obtain uniform shrinkage of the film as a whole. Consequently, as FIG. 12 illustrates, a large number of creases develop around the lower periphery of the resulting package due to a difference in film shrinkage between the top and side portions of the package on one hand and the bottom portion thereof on the other, which fact renders the appearance of the package unsightly.
In the case where the film 4 is thin and flexible, it is necessary that hot air used in film heating should, as FIG. 13 shows, be uniformly blown toward film ends from the top and bottom directions as indicated by arrows A in order to allow autocut film ends 42, 42a to be set neatly along sides of the article 9.
However, the prior art technique involves a problem such that hot air blasting toward the lower film ends 42 is prevented by the belt 41 of the conveyor 40, so that the film ends 42a are shrunk as they remain held apart from the sides of the article. Therefore, as FIG. 12 shows, the lower ends 42a of the film sag, thus making the appearance of the package all the more unsightly.